In recent years, there has been an increasing number of surgeons using surgical staples, rather than conventional sutures. This is true because the use of surgical staples and surgical stapling instruments has made many difficult procedures much simpler to perform. Of more importance, however, is that the use of surgical staples significantly reduces the time required for most procedures, and therefore reduces the length of time which the patient must be maintained under anesthetic. Many types of surgical stapling instruments have been devised for different surgical procedures.
The present invention is directed to a surgical instrument for applying surgical fasteners to internal organs and tissues such as the lung, esophagus, stomach, duodenum, and intestines. The invention is embodied in a linear surgical stapler which permits access to restricted surgical sites, e.g., the pelvic area of the human body.
In its earliest form, the linear surgical stapling instrument was a permanent, multi-use instrument and the surgical staples were manually loaded into the instrument one at a time. An example of a surgical stapling instrument of this type is disclosed in U.S. Pat. No. 3,080,564. This type of instrument was, in general, complex in construction, expensive to manufacture, heavy, bulky and difficult to both load the surgical staples and to clean and sterilize after each use. A subsequent improvement in linear surgical stapling instruments was the provision of presterilized, disposable loading units or staple cartridges. U.S. Pat. Nos. 3,275,211, 3,315,863 and 3,589,589 disclose examples of permanent, multi-use linear instruments having replaceable staple cartridges.
Several types of surgical fastener applying instruments are known for applying surgical fasteners to body tissue clamped between relatively movable fastener holding and anvil portions of the instrument. The surgical fasteners may be metal staples as shown, for example, in U.S. Pat. No. 3,275,211, or consist of non-metallic resinous materials as shown, for example, in U.S. Pat. No. 4,402,445. In the case of metal staples, the staple legs are typically driven through the tissue and formed by the anvil to secure the staples in the tissue. In the case of non-metallic fasteners, each fastener may initially consist of two separate parts, i.e., a fastener part disposed in the fastener holding part of the apparatus, and a retainer part disposed in the anvil part of the apparatus. The leg or legs of the fastener parts are driven through the tissue and interlock with the retainer parts to secure the fasteners in the tissue. Although most surgical staples are biologically inert and remain permanently in the body, biologically absorbable metal surgical staples are known. Surgical fasteners of nonmetallic resinous materials can also be made either biologically absorbable or non-absorbable.
The surgical instrument of the present invention is not limited to use with any particular type or form of fasteners. The various surgical fasteners mentioned above represent examples of the types of fasteners which can be used with the instrument of the present invention. Thus, as used herein, surgical fastener is meant to be generic to all of the above fasteners, including both staples and two-part devices. Similarly, as used herein, fastener holder and anvil are terms which are generic to surgical instruments for applying the above types of fasteners.
In the prior instruments disclosed in U.S. Pat. Nos. 3,275,211 and 4,402,445 for applying surgical fasteners to tissue clamped between the fastener holding and anvil portions of the instrument, a distal fastener applying assembly is rigidly connected to the proximal actuator portion of the instrument. More recently, however, there has been increasing interest in instruments in which the connection between the fastener applying assembly and the actuator assembly is not completely rigid. U.S. Pat. No. 4,473,077, for example, shows a surgical stapler in which the shaft assembly connected between the fastener applying and actuator assemblies is transversely flexible in a single plane.
Also, in view of rising hospital costs, there has been an ever increasing interest in disposable surgical stapling instruments to eliminate as much work as possible, i.e., disassembly, cleaning, reassembly, sterilization and the like, and to be more efficient, while at the same time, not having to compromise the Surgical procedures. U.S. Pat. Nos. 4,354,628, 4,383,634 and 4,527,724, for example, each disclose disposable linear surgical stapling instruments. A surgical fastener applying apparatus is disclosed in U.S. Pat. No. 4,566,620 including a fastener applying assembly rotatably mounted at the distal end of a longitudinal shaft assembly by a joint for allowing rotation of the fastener applying assembly relative to the actuator assembly about each of three mutually orthogonal axes. U.S. Pat. Nos. 4,728,020 and 4,869,414 also disclose surgical fastener applying instruments.
Additional examples of surgical instruments including a fastener applying assembly provided with relatively movable fastener holding and anvil portions are disclosed in U.S. Pat. Nos. 4,591,085 and 4,941,623. The instrument disclosed in U.S. Pat. No. 4,591,085 includes a trigger interlocking mechanism which precludes the actuation of the trigger until an appropriate gap is set between the jaws of the instrument.
U.S. Pat. No. 4,938,408 discloses a surgical stapling instrument including a rotatable support shaft on which a Stapler head is rotatably mounted for rotation about an axis normal to the axis of the support shaft. U.S. Pat. No. 5,137,198 discloses a linear surgical stapling instrument including a fast jaw closure mechanism and a trigger safety device.
In co-pending U.S. patent application Ser. No. 832,299, filed on Feb. 7, 1992, entitled "Surgical Anastomosis Stapling Instrument With Flexible Support Shaft And Anvil Adjusting Mechanism", assigned to the same assignee as the present invention, a surgical stapling instrument including a flexible shaft assembly is disclosed. The flexible shaft assembly comprises a pair of elongated helical elements which are concentrically wound together with the coils of the first helical element alternately interspersed with the coils of the second helical element. Each coil of the first helical element has a round cross section and each coil of the second helical element has a triangular cross section provided with sloped surfaces which slidably engage the adjacent round coils.
In co-pending U.S. patent application Ser. No. 162,557, filed on Dec. 6, 1993, entitled "Surgical Stapling Instrument With Articulated Stapling Head Assembly On Rotatable And Flexible Support Shaft", assigned to the same assignee as the present invention, a surgical stapling instrument is disclosed which includes an actuator handle assembly with a pivotally mounted jaw closure lever and a staple firing lever pivotally mounted on the jaw closure lever. The jaw closure lever operates a closure cable for closing the jaws of a stapling head assembly to clamp the tissue therein. The staple firing lever operates a firing cable for actuating a staple driver to drive surgical staples from a staple holder into the clamped tissue. A pulley is rotatably mounted on the jaw closure lever. The firing cable travels around the pulley and is secured to the staple firing lever which applies tension to the firing cable when the staple firing lever is actuated. The pulley is not Secured to the firing cable and is not coupled by any drive mechanism for rotation by the staple firing lever.
In manually operated medical instruments, e.g. surgical staplers, it is advantageous to operate within the hand strength and grasp size limitations of the persons who will actually operate the instruments. With many medical instrument functions, such as staple firing, the force or load applied to the actuator cable is nonuniform over the required firing stroke. The load is low during early portions of the stroke when the staples are advancing out of the cartridge and piercing the tissue. Once the staples bottom in the anvil pockets, the resistance and load rise rapidly as the staple legs buckle. Then the resistance and load drop down and rise again as the final forming of the staples into a B-shaped configuration occurs. In contrast, the operator has maximum effective strength at the mid-portion of the stroke of the instrument. At the final portion of the stroke, it is advantageous to require a lower operating force to make it easier to over-travel another lever for reopening of the instrument. In addition, it is easier for the operator to complete the firing stroke if the input load drops off at the end of the stroke.
Accordingly, it is an object of the present invention to provide a surgical instrument for applying surgical fasteners, such as surgical staples, with an improved actuator mechanism which operates within the hand strength and grasp size limitations of the operator.
Another object of the invention is to provide a surgical stapling instrument with an improved actuator mechanism in which a pulley is secured to an actuator cable and rotated by a staple firing lever to fire the staples.
It is also an object of the invention to provide a surgical stapling instrument with an improved actuator mechanism which includes a cam pulley secured to a actuator cable and rotatable by a staple firing lever for operating the actuator cable with different mechanical advantages as the cam pulley is rotated to fire the staples.
A further object of the invention is to provide a surgical stapling instrument with an improved actuator mechanism including a cam pulley secured to an actuator cable and rotatable by a staple firing lever which includes an anti-backup mechanism to prevent the pay-out of the actuator cable before and after the staples are fired.